1. Field of the Invention
The present invention relates to rotary cutting tools chiefly for use in surface cutting such as, for example, a face milling cutter or the like and, more particularly, to a rotary cutting tool capable of successively processing chips generated during cutting.
2. Prior Art
Tools of various configurations have conventionally been proposed as rotatable cutting tools which are used to apply surface processing to a workpiece. Of the tools, a tool for use in a face milling cutter is small in cutting resistance and is suitable for strong cutting. Accordingly, the tool for use in the face milling cutter has widely been utilized at present.
The tool for the face milling cutter comprises a cutter body rotatable about its rotational axis, a plurality of face cutting edges provided at the forward end face of the cutter body, and a plurality of outer peripheral cutting edges provided at a forward end of an outer peripheral surface of the cutter body. Generally, these edges are made of cemented carbide. Almost all mounting methods of the cutting edges use throw-away methods in which at least one carbide tip having the cutting edges is fixedly mounted to the cutting body in a detachable manner. Thus, as the conventional tool for the face milling cutter, an example of the tool for the face milling cutter of throw-away type will be taken and will be described with reference to FIGS. 76 through 78 of the attached drawings.
As shown in FIGS. 76 and 77, a cutter body 1 is generally cylindrical in shape and has, at its proximal end, a diameter-reduced section. The cutter body 1 has a forward end whose outer periphery is formed with a plurality of recesses or tip mounting grooves 2. The tip mounting grooves 2 open toward the forward end of the cutter body 1 and toward a location radially outwardly thereof. The tip mounting grooves 2 are equidistantly spaced from each other along the peripheral direction of the cutter body 1. A plurality of throw-away tips (hereinafter referred simply to as "tips") 3 are mounted respectively within the tip mounting groove 2 by their respective clamp mechanisms 6. Each of the clamp mechanisms 6 comprises a wedge element 4 and a clamp screw 5 as shown in FIG. 78. By the clamp mechanism 6, the tip 3 is urged against one of a pair of opposed wall surfaces of the tip clamp groove 2, whereby the tip 3 is fixedly mounted in position to the cutter body 1 in a detachable manner.
As shown in FIG. 78, the tip 3 is in the form of a plate element made of cemented carbide and is in plan generally square in shape. When the tip 3 is fixedly mounted in position to the tip mounting groove 2, one end of the tip 3, which projects from the forward end face of the cutter body 1, is formed into a face cutting edge 3a, and one side of the tip 3, which projects from the forward end of the outer peripheral surface of the cutter body 1, is formed into an outer peripheral cutting edge 3b.
As shown in FIGS. 77 and 78, a plurality of tip pockets 7 are provided respectively in front of the tips 3 in the rotational direction of the cutter body 1. Each of the tip pockets 7 opens toward the forward end of the cutter body 1 and toward the radially outward location thereof, and has an arcuate wall surface. The tip pocket 7 has such a function as to successively guide and discharge chips generated by the cutting edges 3a and 3b, to the outside of the cutter body 1. Further, when a workpiece W is made of material which tends to generate continuous streamline chips such as low carbon steel or the like, the tip pocket 7 has also such a function of continuously rounding off the chips generated, and to divide and to break the chips.
On the other hand, the diameter-reduced section of the cutter body 1 is fixedly mounted to an arbor 8 through a detent key 9. Specifically, the arbor 8 has a shaft section 8a which is fitted in a mounting bore 10 which is formed at the center of the diameter-reduced section of the cutter body 1. A fastening bolt 11 is screwed into the end face of the shaft section 8a from an end face of the diameter-reduced section of the cutter body 1, which is located adjacent a larger-diameter section of the cutter body 1. In this manner, the cutter body 1 is fixedly mounted to the arbor 8 in concentric or coaxial relation thereto. Furthermore, at a location opposite to the shaft section 8a, the arbor 8 has a tapered shank 8b which is fitted in a tapered bore 12a in a main spindle 12 of a machine tool (hereinafter referred to as "main spindle"). The tapered shank 8b has its forward end which is formed with a female thread section (not shown). The female thread section is provided for drawing or pulling up the arbor 8 axially of the main spindle 12 by means of a drawing bolt (not shown) within the main spindle 12, to firmly connect the face milling cutter and the main spindle 12 to each other.
Face processing of the workpiece W by the use of the tool for the face milling cutter constructed as above is conducted as follows.
As shown in FIG. 76, the taper shank 8b of the arbor 8 is first fitted in the tapered bore 12a of the main spindle 12. The arbor 8 is drawn axially of the main spindle 12 by the drawing bolt. The arbor 8 is fixedly mounted to the main spindle 12 through a pair of main spindle keys 13. Thus, the face milling cutter is mounted to the main spindle 12. Subsequently, the workpiece W is fixedly mounted to a machine table (not shown) such that a work surface of the workpiece W extends perpendicularly to the axis of the main spindle 12. The main spindle 12 is rotated about its axis. The main spindle 12 or the machine table is moved axially of the main spindle 12 to give a predetermined depth of cut to the surface of the workpiece W. The main spindle 12 or the machine table is moved in a direction perpendicular to the axis of the main spindle 12. By doing so, surface parts of the workpiece W are successively cut by the face cutting edge 3a and the outer peripheral cutting edge 3b of each of the tips 3, so that the workpiece W is subject to surface processing.
The face milling cutter described above has the following drawback or disadvantage. That is, since the face milling cutter merely guides and discharges the chips generated, peripherally outwardly of the face milling cutter, the chips are widely dispersed or scattered to the circumference of the face milling cutter, accompanied with rotation of the cutter body 1. As a result, not only is the operational environment deteriorated, but also hazardous operating conditions sometimes occur. Further, a considerable time is taken to process the chips after completion of the cutting.
Moreover, the conventional face milling cutter has also the following disadvantage. That is, since the chips are gradually accumulated on the workpiece W, the table of the machine or the like, as the cutting continues, thermal deformation occurs in the workpiece W or the machine due to heat of the chips. Thus, working or processing accuracy is deteriorated, and the chips bit into the tip 3 so that the quality of the cut surface is damaged.
Furthermore, the chips scattered to the environment of the machine get into a sliding surface or the like of the machine. Thus, there is a fear that the machine per se deteriorates in accuracy or has its service life reduced.
The above-discussed problems are particularly important at a machining center which requires unmanned operation for a long period of time.
Further, in the case where the conventional face milling cutter described above is used to process a joint surface of a box-type workpiece having a relatively thin wall thickness, or to process a workpiece such as an opposite or reverse boss in which portions relatively small in processing area are dotted, there is a case where the width of the processing surface extending along the rotational direction of the tool becomes narrower than the peripheral pitch of the tips 3. In this case, since the tips 3 are cut intermittently into the workpiece, the cutting force fluctuates violently so that sheaves or shakes and vibration are induced.
In addition, intermittent contact between the tips 3 and the workpiece also causes periodical fluctuation in the dynamic rigidity of the main spindle system of the machine to which the tool is mounted. Thus, the sheaves or shakes and vibration induced by the cutting are amplified to cause breakage of the cutting edges and to reduce the service life thereof and, further, to cause a reduction in the processing accuracy of the workpiece. Thus, there is a fear that normal or regular cutting processing is damaging.